Experiment 5 - Chem 14.1 Preparation Identification and...

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Chem 14.1: Preparation, Identification and Properties of Colloids Page 1 of 5 Preparation, Identification and Properties of Colloids BUENDIA, Maria Andrea M. NICDAO, Deborah S. March 15, 2016 Abstract Colloids are mixtures which exhibit intermediate properties between heterogeneous and homogeneous mixtures. This study focuses on identifying different kinds of colloids and comparing some methods of preparing colloids, namely, condensation and dispersion. Colloidal properties such Tyndall effect and precipitation were also observed in this study. In the first part of the experiment, sols (solid dispersed in liquid) such as Fe(OH) 3 and sulfur sol, and emulsion (liquid dispersed in liquid) were prepared. The sols were classified as lyophobic, solvent-hating, or lyophilic, solvent-loving. Fe(OH) 3 and sulfur sol are both lyophobic and were prepared using the dispersion and condensation method, respectively. In addition, oil in water emulsion was prepared and concentrated soap solution was used as the emulsifying agent. In the second part of the experiment, different mixtures were prepared and indication of Tyndall effect was tested. Only the CuSO 4 solution, unboiled starch solution and distilled water did not exhibit Tyndall effect. In the last part of the experiment, precipitation was observed by comparing the amount of precipitate formed by adding 10 drops of different precipitants (NaNO 3 , Na 2 SO 4 and Na 3 PO 4 ) to Fe(OH) 3 . The results showed that Na 3 PO 4, which produced the most amount of precipitate, is the strongest electrolyte among the three precipitants. Keywords: colloids, Tyndall Effect, precipitation, condensation, dispersion I. Introduction Colloids are intermediate types of dispersions whose particles are larger than typical molecules but not so large that the components of the mixture separate under the influence of gravity (Brown, et al, 2012, p. 541). The particles in a colloid, called the dispersed phase, have dimensions approximately between 1-1000 nm and may be spherical, either rod-shaped such as those in colloidal silica or disc-shaped such as those in gamma globulin in human blood plasma (Petrucci, 2011, pp. 585-586). The medium in which the particles disperse is called the dispersing phase. Colloids are generally classified on the basis of the component phases (Karnataka, 2008). Table 1 below shows the different kinds of colloids based on the individual physical states of the dispersed phase and dispersing medium. Table 1. Classification of colloids based on component phases Dispersed Phase Dispersing Medium Solid Liquid Gas Solid Solid sol Sol Aerosol Liquid Solid emulsion Emulsion Aerosol Gas Solid foam Foam - Retrieved from Petrucci, 2008, p. 589 Another classification of colloids would be based on the affinity or interaction between the dispersed and dispersing phases namely, lyophobic, or solvent-hating colloid, and lyophilic, or solvent-loving colloid.
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